This invention relates to a new catalyst composition useful for initiating and promoting polymerization of .alpha.-olefins and to a polymerization process employing such a catalyst composition.
It is well known that olefins such as ethylene, propylene, and 1-butene can be polymerized in the presence of metallic catalysts, particularly the reaction products of organometallic compounds and transition metal compounds to form substantially unbranched polymers of relatively high molecular weight. Typically such polymerizations are carried out at relatively low temperatures and pressures. The resulting generally linear olefin polymers are characterized by greater stiffness and higher density than olefin polymers having highly branched polymer chains.
Among the methods for producing linear olefin polymers, some of the most widely utilized are those described by Professor Karl Ziegler in U.S. Pat. No. 3,113,115 and 3,257,332. In these methods, the catalyst employed is obtained by admixing a compound of a transition metal of Groups 4b, 5b, 6b and 8 of Mendeleev's Periodic Table of Elements with an organometallic compound. Generally the halides and oxyhalides of titanium, vanadium and zirconium are the most widely used transition metal compounds. Outstanding examples of the organometallic compounds include hydrides, alkyls and haloalkyls of aluminum, alkyl aluminum halides, Grignard reagents, alkali metal aluminum hydrides, alkali metal borohydrides, alkali metal hydrides, alkaline earth metal hydrides and the like.
Usually, polymerization is carried out in a reaction medium comprising an inert organic liquid, e.g., an aliphatic hydrocarbon, and the aforementioned catalyst. One or more olefins may be brought into contact with the reaction medium in any suitable manner, and a molecular weight regulator, which is normally hydrogen, is usually present in the reaction vessel in order to suppress the formation of undesirably high molecular weight polymers.
Following polymerization, it is common to remove catalyst residue from the polymer by separating the polymer from the inert liquid diluent and then repeatedly treating the polymer with an alcohol or similar deactivating agent. Such catalyst deactivation and/or removal procedures are expensive both in time and material consumed as well as the equipment required to carry out such treatment.
Furthermore, most of the aforementioned known catalyst systems are more efficient in preparing polyolefins in slurry (i.e., wherein the polymer is not dissolved in the carrier) than in solution (i.e., wherein the temperature is high enough to solubilize the polymer in the carrier). The lower efficiencies of such catalysts in solution polymerization is generally believed to be caused by the general tendency of such catalyst to become rapidly depleted or deactivated by significantly higher temperatures than are normally employed in solution processes.
In view of the expense of removing catalyst residues from the polymer, it would be highly desirable to provide a polymerization catalyst which is sufficiently active, even at solution polymerization temperatures, to produce such high quantities of polymer per unit of catalyst that it is no longer necessary to remove catalyst residue in order to obtain polymer of the desired purity.